查看更多>>摘要：Rare earth-based functional perovskites have received significant attention due to increasing energy crisis problems and environmental pollution.Many non-toxic,lead-free materials have been investi-gated;bismuth sodium titanate(Bi0.5Na0.5TiO3)has gotten significant attention because of its unique morphological,structural,and electrical properties.Also,the emergence of bismuth sodium titanate with a high remnant polarization has revived the application of inorganic materials in electronic devices.This type of ferroelectrics is known to display new functionalities coupled with ferroic orders.In recent years,research in the field of inorganic-based ferroelectrics,mainly Bi0.5Na0.5TiO3(BNT),has been thriving toward enhanced electronic device performance.Doping rare earth elements in BNT compounds has achieved significant electrical properties.This article summarizes prominent theories associated with ferroelectric-dielectric mechanisms and provides the most recent progress in rare earth-based BNT systems.Emphasis is placed on design of principles toward tailoring the crystal structure via doping effect and oxygen vacancies,as well as domain engineering.Finally,the critical investigation is accom-panied by future perspectives,including integrating rare earth BNT perovskites for high-performance ferroelectric devices.
查看更多>>摘要：Lanthanum-doped double halide perovskite has attracted increasing interest due to its distinctive up-conversion and near-infrared(NIR)luminous characteristics.Here,erbium ion(Er3+)doped Cs2(Na/Ag)BiCl6 microcrystals(MCs)were synthesized and proved to be one of the most prospective candidates for optical thermometry.The enhancement of both white light from self-trapped exciton emission and NIR emission from Er3+ion of Cs2AgBiCl6 microcrystals is caused by lattice distortion due to Na+ion doping.Fluorescence intensity ratio and lifetime methods provide self-referenced and sensitive thermometry under 405 and/or 980 nm laser excitation at the temperatures from 80 to 480 K.Besides,the maximum values of relative and absolute sensitivity of 3.62％/K and 27％/K can be achieved in the low to high temperature range under 980 and 405 nm laser co-excitation.Through the experimental analysis,Er3+doped Cs2(Na/Ag)BiCl6 double perovskite is considered to be an ideal self-calibrating thermometric material due to its good long-term stability and multi-mode function of excitation and detection.
查看更多>>摘要：Upconversion based nanothermometry has received much attention due to its merits of stability,narrow band emission and rich emission peaks.However,the previous works are mainly focused on the emis-sions from thermally coupled energy levels which is theoretically limited by Boltzmann distribution theory with resultant low temperature sensitivity in particular at ultralow temperatures.Here we report a LiYF4∶Yb/Ho@LiYF4 core-shell nanostructure to improve the sensitivity at low temperatures by taking advantage of non-thermally coupled energy levels of Ho3+.In detail,the green upconversion emission of Ho3+shows an increase with reducing temperature while its red upconversion emission presents a decline during the same process.This is primarily due to the suppression of the non-radiative multi-phonon relaxation occurred at the green emitting levels(5F4,5S2)and the intermediate level(5I6)at low temperatures.Such a feature contributes to a high relative sensitivity of 7.17％/K at 11 K,much higher than reported values.Our results provide a promising candidate for the development of nano-thermometer with high-sensitive low-temperature sensing performance.
查看更多>>摘要：In this research,a series of Sm3+doped CsLu(WO4)2 phosphors was prepared via high temperature solid phase technique to design new red phosphors and optical thermometric materials.Their structures,morphology,band gap and luminescence properties were characterized by X-ray diffraction,scanning electron microscopy,diffuse reflection and luminescence spectra,respectively.Under UV excitation,CsLu(WO4)2 gives rise to a blue broad emission band between 350 and 700 nm,which stems from the 3T1u→ 1A1g transition of WO66-groups.When Sm3+is introduced into CsLu(WO4)2,energy transfer between WO66-groups and Sm3+ions takes place in CsLu(WO4)2∶Sm3+phosphors,and color-tunable luminescence from blue to red is realized by controlling the Sm3+doping concentration.The energy transfer efficiency between WO66-groups and Sm3+ions was analyzed,and the energy transfer mechanism was determined to be dipole-dipole interactions.According to the temperature-dependent luminescence spectra,WO66-groups and Sm3+ions exhibit large discrepancy in thermal quenching rates,and thus the temperature sensing properties of CsLu(WO4)2∶Sm3+in the temperature range of 283-403 K were analyzed.Based on the framework of fluorescence intensity ratio theory,the basic optical thermometry parameters including absolute and relative sensitivity of CsLu(WO4)2∶Sm3+were calculated and the results show that it has great potential for application in optical thermometry.
查看更多>>摘要：Lead-free halide double perovskite has received widespread attention due to its excellent optical per-formance.However,the lack of deep red light and poor heat quenching resistance severely limit its application in plant lighting field.In this work,Ho3+was introduced into the thermally stable Cs2NaScCl6 host,exhibiting a deep red emission of 660 nm.By constructing an energy transfer channel between Sb3+and Ho3+,the photoluminescence quantum yield(PLQY)of Cs2NaScCl6∶1％Sb3+,40％Ho3+rises up to 53.8％,that is increased by 17 times,and its emission intensity can still be maintained by 80％at 423 K,exhibiting good heat quenching resistance.The obtained Cs2NaScCl6∶1％Sb3+,40％Ho3+and Cs2NaScCl6∶1％Sb3+with blue light emission were employed for fabricating a light-emitting diode(LED)device with a 340 nm UV chip,and its emission spectrum matches well the absorption spectra of chlorophyll A and chlorophyll B with the high resemblance of 70％and 75％,making it suitable for use as an artificial light source to control the growth process of plants in the field of plant lighting.
查看更多>>摘要：The pursuit of high-brightness solid-state lighting(SSL)stimulates the development of all-inorganic color converters with high robustness.It is required that the fluorescent material is able to cope with the extreme condition generated from the irradiation of high-power-density excitation light.As such,in this work,we developed a new composite color converter,i.e.,Y3Al5O12∶Ce3+phosphor-in-silica glass ceramic(YAG:Ce3+PiSGC).Remarkably,the amorphous SiO2 matrix spontaneously transforms into tetragonal SiO2 crystallites during co-sintering with crystallization fraction reaching up to＞90％(almost full ceramization).The activation energy for crystallization Ec and Avrami index n of amorphous silica oxide are 298.5 kJ/mol and 1.71,indicating the diffusion-controlled glass crystallization mechanism.The fabricated prototype high-power phosphor-converted white light-emitting diode(pc-wLED)and phosphor-converted white laser diode(pc-wLD)based on YAG:Ce3+PiSGC show satisfactory photo-metric/colorimetric parameters.The developed color converters have combined merits of environmental protection property,cost-effective manufacturing,good luminescent performance,and easy scalability.This study highlights a new kind of opto-functional composite material and its application as an efficient color converter in high-power solid-state lightings.
查看更多>>摘要：A series of Dy3+/Eu3+single doped and co-doped SrLaAlO4 phosphors was synthesized by the traditional high-temperature solid-state method,and their structure,morphology and optical properties were characterized.The X-ray diffraction(XRD)shows a small amount of doping with Dy3+and Eu3+does not change the crystal structure of the matrix SrLaAlO4 and the best synthesis temperature is 1450 ℃.The scanning electron microscopy(SEM)indicates the particle size directly ranges from 1 to 5 μm roughly and the energy dispersive spectroscopy(EDS)patterns show that SrLaAlO4∶Dy3+phosphor and SrLaAlO4∶Dy3+,Eu3+phosphor were successfully synthesized.SrLaAlO4∶Dy3+phosphor can be effectively excited by near-ultraviolet light,producing two strong emission lights at 483 nm(blue light)and 579 nm(yellow light),presenting a cold white light;SrLaAlO4∶Eu3+phosphor can be effectively excited by near-ultraviolet light,producing red lights at 622 nm;the characteristic emission peaks of Dy3+and Eu3+can be shown simultaneously under the same excitation wavelength in SrLaAlO4∶Dy3+,Eu3+phosphor.By changing the relative doping concentration ratio of Dy3+and Eu3+,the modulation of SrLaAlO4∶Dy3+,Eu3+phosphor from cold white to warm white light can be achieved.In addition,the study of the luminescent mechanism and lifetime shows that there is energy transfer between Dy3+and Eu3+in SrLaAlO4∶Dy3+,Eu3+phosphor.
查看更多>>摘要：The catalytic behavior of a catalyst for chlorine-containing volatile organic compounds(CVOCs)oxidation largely depends on the synergistic interaction between the oxidizing and acidic sites.In the present work,two catalysts with different distributions of CeO2 on the inner and outer surfaces of 4.0Ce-USY-ex and 4.0Ce-USY-dp(USY zeolite)were prepared respectively by ion exchange and deposition methods,with a purpose of finding out how the location of the oxidation sites(CeO2)influence its synergistic effect with the acidic sites of zeolite.The results show that 4.0Ce-USY-ex is much more active for catalytic degradation of 1,2-dichloroethane(DCE),while 4.0Ce-USY-dp catalyst exhibit higher catalytic degrada-tion activity for other structured CVOCs(dichloromethane(DCM),trichloroethylene(TCE),chloroben-zene(CB)).CeO2 in 4.0Ce-USY-ex catalyst mainly disperses in the pore channels of USY zeolite,and there are many strong acid centers on the surface,which is conducive to the dechlorination conversion of CVOCs.However,CeO2 in 4.0Ce-USY-dp catalyst is mainly distributed on the outer surface of USY and has strong oxidation ability,which contributes to the deep oxidation of CVOCs.Moreover,the presence of a large number of strong acid centers on the catalyst surface of 4.0Ce-USY-ex catalysts leads to severe accumulation of surface carbon species and significantly decreases its stability towards DCE.However,a large number of active oxygen species on the surface of 4.0Ce-USY-dp and CeO2 catalysts are beneficial to the deep oxidation of DCE,reducing the formation of surface carbon and thus improving the stability of the catalyst.Thus,the influence of the location of the oxidation sites on its synergistic effect with the acidic sites was established in the present work,which could provide some new ideas for the rational design of CVOCs degradation catalyst with appropriate distribution of active sites.
查看更多>>摘要：Rare earth metal based perovskite emerges as important catalytic material for energy production and storage.These ABO3 type materials are now the focus of research in the field of oxygen reduction and evolution reactions.Here,in this work we evaluated the oxygen reduction properties of the synthesized one-dimensional REMnO3(RE=Pr,Nd,Sm,Eu and Gd).The one-dimensional REMnO3 prepared by the hydrothermal synthesis route results in pure phase perovskite on calcinations.The perovskite was characterized with X-ray diffraction,Fourier transform-infrared(FT-IR),field emission-scanning electron microscopy(FE-SEM),transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).The oxygen reduction reaction activities were investigated with the help of electrochemical workstation that consists of three-electrode system immersed in 0.1 mol/L KOH electrolyte solution saturated with oxygen.The Koutechy-Levich plot obtained from rotating ring disk electrode shows all the prepared catalysts follow 4e processes during oxygen reduction.The effect of"A"site cation vari-ation in REMnO3 on oxygen reduction reaction is discussed.SmMnO3 showed better onset potential for oxygen reduction reaction among the prepared rare earth perovskite.SmMnO3 having high RE:Mn ratio(A-site rich compositions)promotes oxygen reduction reaction(ORR)activity.All the perovskites showed good oxygen reduction property with high stability and methanol tolerance.
查看更多>>摘要：By using a rigid bulky carboxylic ligand α-cyanocinnamic acid(CCA),a dinuclear dysprosium(Ⅲ)com-plex[Dy2(CCA)6(MeOH)4](1)was synthesized.Single crystal X-ray crystallography reveals that the two eight-coordinate dysprosium ions are bridged by four deprotonated carboxyl groups,forming a centrosymmetric paddle-wheel-like structure.Dynamic magnetic property measurements indicate that complex 1 displays field-induced slow magnetic relaxation.The temperature-dependent relaxation times can be fitted using Orbach and Raman processes with parameters of n=2.8(2),C=27(8)s-1/Kn,τ0=5(2)x 10-10 s and Ueff=40(3)cm-1.Magnetic studies on the diamagnetic YⅢ-diluted analogue[Dy0.206Y1.794(CCA)6(MeOH)4](2)reveal its slow magnetic relaxation behavior without external dc field and the antiferromagnetic coupling between the DyⅢ ions in 1.Fits on the obtained relaxation times of 2 lead to the parameters of n=4.5(3),C=0.7(2)s-1/Kn,τ0=2.8(2)× 10-9 s and Ueff=38(2)cm-1.The results suggest that slow magnetic relaxation originates from the single-ion relaxation of DyⅢ ions.Moreover,the diamagnetic dilution can suppress other fast relaxation pathways at low temperature,on account of the elimination of magnetic coupling and dipolar interaction.Ab initio calculations were then performed on the single DyⅢ ion species {YDy} and indicate that the first excited Kramers doublets(KDs)lie at ca.76 cm-1,which is slightly higher than the experimental Ueff value.The intramolecular magnetic interactions were also calculated and indicate a weak ferromagnetic dipole-diploe magnetic interaction and an antiferromagnetic exchange coupling.
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